The Gambusia affinis, a small, subtropical fish that eats mosquito larvae, is being used in California, Arizona, Florida and other areas dealing with the rising number of foreclosures, reports The Wall Street Journal.

“They are real heroes,” says Josefa Cabada, a technician for a government pest control agency in Contra Costa, Calif. “I’ve never seen a mosquito in a pool with mosquito fish.”

The hardy fish, which are often used to keep garden ponds mosquito-free, can survive in the swimming pools for months, eating up to 500 larvae a day.

Officials concerned that infested pools could lead to disease outbreaks say that the fish prevent crews from having to use pesticides, keeping pools safe during the lengthy foreclosure process. So many homes are involved that some agencies are hiring planes to locate and photograph abandoned pools from the air.

But some scientists argue that the Gambusia affinis can be harmful to ecosystems when introduced into ponds and rivers, and advocate for using native fish species to combat mosquito problems.

The “mosquito fish” phenomenon is just one of the more unusual ramifications of the sub-prime mortgage crisis in the United States, which has forced families from their homes and affected credit, jobs, consumer spending, and financial institutions. The effects have even spread to countries abroad.

Government officials are extolling the use of the Gambusia affinis to clean up pools of foreclosed homes. The fish have been used for decades to control mosquito populations in cattle ponds, irrigation ditches and decorative ponds.

The effects of the U.S. mortgage crisis have gone global. Last month, markets in real-estate heavy countries such as Ireland and Spain were reeling from the slowdown. Related industries were also hurting: fewer home sales have meant fewer furniture shoppers for businesses like Swedish furniture-maker Ikea, which reported a decline in sales across Europe as.

The Gambusia Control Homepage argues that introducing “mosquito fish” can be potentially harmful to native fish populations and other invertebrate populations and can have an adverse effect on certain ecosystems. It claims that most fish will eat mosquito larvae and that using native fish local to the area is a better alternative.

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